Infusion device and driving mechanism for same

ABSTRACT

A drive mechanism for delivery of infusion medium has a coil and an armature moveable toward a forward position, in response to the electromagnetic field produced by activation of the coil. A piston is moveable axially within a piston channel to a forward position, in response to movement of the armature to its forward position. The armature and piston are moved toward a retracted position, when the coil is not energized. In the retracted position of the piston, a piston chamber is formed between the piston and a valve member and is filled with infusion medium. As the piston is moved to its forward position, the piston chamber volume is reduced and pressure within the piston chamber increases to a point where the pressure moves the valve member into an open position through an outlet.

CROSS-REFERENCE TO RELATED APPLICATIONS

Embodiments of the present invention claim priority from a U.S.Provisional Application entitled “Infusion Device and Driving MechanismFor Same,” Ser. No. 60/317,886, filed Sep. 7, 2001, the contents ofwhich are incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to infusion devices, systems andprocesses and, in particular embodiments to implantable infusiondevices, systems and processes employing a drive mechanism configurationwhich allows the device to have a relatively thin form factor and usepower efficiently. Further embodiments of the invention relate to drivemechanisms and processes of making and using such drive mechanisms forinfusion devices and systems.

RELATED ART

Infusion devices are typically used to deliver an infusion media, suchas a medication, to a patient. Implantable infusion devices are designedto be implanted in a patient's body, to administer an infusion media tothe patient at a regulated dosage.

Because implantable infusion devices are designed to be implanted in thepatient's body, the dimensions of such devices can have an impact on thedetermination of the location in the body at which a device may beimplanted, the level of comfort of the implant patient and the externalappearance of the implant site. Typically, a device with relativelysmall dimensions and, in particular, a relatively small thickness formfactor, will provide greater flexibility in the choice of location inthe patient's body to place the implant and will minimize patientdiscomfort and minimize noticeable protrusions at the implant site.Accordingly, there is a demand in the industry for minimizing theoverall dimensions, and, in particular, the thickness dimension ofimplantable infusion device.

In some contexts of use, the infusion device must be operable for anextended period with a limited power supply. For example, batterypowered infusion devices may be implanted in or otherwise connected topatients, to deliver medication at controlled intervals over a prolongedperiod of time. In some devices, when the batteries die, the devices aresimply thrown away. Also, as the battery power supplies for such deviceshave limited capacities, some devices typically require multiplereplacements of batteries over their operational life. There is a demandin the industry for infusion devices which make efficient use of powersupplies and, thus, require fewer or no power supply replacements. Thisdemand is particularly important for implantable devices, which mayrequire surgical removal to replace depleted power supplies.

SUMMARY OF THE DISCLOSURE

Accordingly, embodiments of the present invention relate to infusiondevices and drive mechanisms for infusion devices which address theabove-mentioned industry demands.

Preferred embodiments of the invention relate to such devices and drivemechanisms configured for implantation in a patient's body.Configurations described herein allow the drive mechanism and, thus, theinfusion device to have a relatively small thickness dimension, forexample, to minimize trauma to the implant recipient (referred to hereinas the patient).

Further preferred embodiments relate to such devices and drivemechanisms configured and operated to make highly efficient use ofelectrical power to prolong operational life.

Yet further preferred embodiments relate to such devices and drivemechanisms configured to deliver relatively precisely controlled volumesof infusion medium, within a relatively wide range of volumes, includingrelatively small volumes.

Yet further preferred embodiments relate to such devices and drivemechanisms configured to deliver sufficiently precise volumes ofrelatively high concentration infusion medium.

An infusion device according to an embodiment of the invention includesa generally disc-shaped housing made from a biocompatible and infusionmedium compatible material. The infusion device housing contains areservoir for holding a volume of infusion medium, such as, but notlimited to, a medication to be administered to the patient. The infusiondevice housing has an outlet through which the infusion medium may beexpelled.

The infusion device further includes a drive mechanism having an inletcoupled in fluid flow communication with the reservoir and an outletcoupled in fluid flow communication with the infusion device housingoutlet. In one embodiment, a filter may be disposed between thereservoir and the drive mechanism (or as part of the inlet of the drivemechanism). In a further embodiment, expandable and compressabledevices, such as one or more volume compensators or accumulators, whichmay also be, for example, accumulators, also may be disposed in the flowpath between the reseervoir and the drive mechanism inlet, to dampensurges and ebbs in the flow.

The drive mechanism employs electromagnetic and mechanical forces tomove a piston between retracted and forward positions or states, tocause infusion medium to be drawn from the reservoir, through an inletand forced out of an outlet. A drive mechanism, according to oneembodiment, comprises an assembly of components which may bemanufactured and assembled in a relatively cost efficient manner. Thecomponents include a housing containing a coil disposed within a coilcup, a piston channel surrounded by the coil, a piston extending throughthe piston channel, an armature disposed at one end of the pistonchannel and an outlet chamber with a valve assembly disposed at theother end of the piston channel.

When the coil is in a quiescent state, the armature and piston are urgedtoward a retracted position by mechanical or magnetic forces. When thecoil is energized, the armature and piston move to a forward strokeposition. The movement of the piston from a retracted position to aforward position creates pressure differentials within the drivemechanism to drive medium out the outlet. Mechanical force may returnthe piston to the retracted position. The movement of the piston from aforward position to a retracted position creates pressure differentialsto draw medium into the drive mechanism inlet.

Embodiments of the invention employ a coaxial arrangement of the piston,the piston channel and the coil, to provide significant advantages withrespect to providing a relatively thin form factor and efficient powerusage. A number of features can each provide or be combined tocontribute to a reduction in the thickness form factor of the drivemechanism. For example, a coaxial arrangement of components can beimplemented with a smaller thickness form factor than alternativearrangements in which components are arranged in series with each otherin the thickness dimension. Embodiments may include an inlet volume onone side of the coil and an outlet chamber on the opposite side of thecoil, with a flow passage through the piston channel, such that the coiland flow channel share a common portion of the thickness dimension. Thearmature may be located within the inlet volume and, thus, share acommon portion of the thickness dimension with the inlet volume. Theoutlet chamber may be centrally located within the same housing that hasthe coil cup and formed in relatively close proximity to the coil cup inthe thickness dimension of the housing.

Further embodiments may include an outlet port and one or more fluidflow damping or accumulator structures, such as pillows or accumulatorsin pillow or accumulator cavities, in the housing, to help provide arelatively stable, constant output pressure during drive operations. Theaccumulator cavities, outlet port and outlet chamber may share a commonportion of the thickness dimension of the drive mechanism, to maintain arelatively thin form factor.

In addition, a number of features described herein can provide, or becombined to contribute to, the efficient use of power to, prolong theoperational life of the drive mechanism. One manner of improving theoperational life of an infusion device according to embodiments of thepresent invention, is to lower the power consumption requirements of thedrive mechanism by employing a coaxial coil and piston configuration andone or more features for making highly efficient use of electromagneticenergy. Another manner of improving the operational life of a deviceaccording to embodiments of the invention is to reduce the number ofoperations of the drive mechanism required over a given period of time,by pumping reduced volumes of a higher concentration infusion medium (aninfusion medium with a higher concentration of active ingredients) orpumping higher concentration volumes at reduced intervals.

These and other aspects and advantages of the invention will be apparentto one of skill in the art from the accompanying detailed descriptionand drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 is a perspective view of an implantable infusion device accordingto an embodiment of the invention.

FIG. 2 is a perspective view of a drive mechanism for an implantableinfusion device according to an embodiment of the invention.

FIG. 3 is a cross-section view of one example embodiment of the drivemechanism of FIG. 2, in a retracted position or state.

FIG. 4 is a cross-section view of the example drive mechanism embodimentof FIG. 3, in a forward stroke position or state.

FIG. 5 is a an exploded view of an embodiment of the drive mechanismshown in FIGS. 3 and 4.

FIG. 6 is a perspective view of an embodiment of the inlet end of ahousing for the drive mechanism in FIGS. 3 and 4.

FIG. 7 is a perspective view of an embodiment of the outlet end of thedrive mechanism housing of FIG. 6.

FIG. 8 is a perspective view of an embodiment of a coil cup for thedrive mechanism in FIGS. 3 and 4.

FIG. 9 is a perspective view of an embodiment of an actuator comprisingan armature and a piston for the drive mechanism in FIGS. 3 and 4.

FIG. 10 is a partial cross-section view of a portion of a drivemechanism housing with an accumulator chamber.

FIG. 11 is a cross-section view of another example embodiment of thedrive mechanism of FIG. 2, in a retracted position or state.

FIG. 12 is a cross-section view of the example drive mechanismembodiment of FIG. 11, in a forward stroke position or state.

FIG. 13 is a partial cross-section view of a portion of the drivemechanism cover, armature and piston, according to a further embodimentof the invention.

FIG. 14 is a cross-section view of a valve assembly structure accordingto a further embodiment of the invention.

FIG. 15 is a cross-section view of a drive mechanism having a valveassembly structure in accordance with the embodiment of FIG. 14.

FIG. 16 is a cross-section view of a valve assembly structure accordingto yet a further embodiment of the invention.

FIG. 17 is a cross-section view of a valve assembly structure accordingto yet a further embodiment of the invention.

FIG. 18 is a cross-section view of a valve assembly structure accordingto yet a further embodiment of the invention.

FIG. 19 is a cross-section view of a valve assembly structure accordingto yet a further embodiment of the invention.

FIG. 20 is a cross-section view of a valve assembly structure accordingto yet a further embodiment of the invention.

FIG. 21 is a cross-section view of a valve assembly structure accordingto yet a further embodiment of the invention.

FIG. 22 is a cross-section view of a valve assembly structure accordingto yet a further embodiment of the invention.

FIG. 23A is a perspective view of an actuator member according to yet afurther embodiment of the invention.

FIG. 23B is a side view of an actuator member covered by a coveringmaterial according to yet a further embodiment of the invention.

FIG. 24 is a plan view of an actuator member according to yet a furtherembodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following detailed description is of the best presently contemplatedmode of implementing the invention. This description is not to be takenin a limiting sense, but is made merely for the purpose of illustratingthe general principles of embodiments of the invention. The scope of theinvention is best defined by the appended claims.

As discussed above, the present invention relates generally to infusiondevices having drive mechanisms and also to drive mechanismconfigurations for infusion of a medium into a patient or otherenvironment. Preferred embodiments of the invention relate to suchdevices and drive mechanisms configured for implantation in a patient'sbody. Configurations described herein allow the drive mechanism and,thus, the infusion device to have a relatively small thicknessdimension, for example, to minimize trauma to the implant recipient(referred to herein as the patient). Further preferred embodimentsrelate to such devices and drive mechanisms configured and operated tomake highly efficient use of electrical power to prolong operationallife.

FIG. 1 shows an implantable infusion device 10 according to anembodiment of the invention. The illustrated device 10 is configured tobe surgically implanted into a patient, for example, in the abdominalregion, between the skin and the abdominal wall. A catheter connected tothe pump may deliver infusion medium to the patient, for example, byfeeding infusion medium to a particular location in the venous system,within the spinal column or in the peritoneal cavity of the patient. Asdescribed below, preferred embodiments of the device 10 are configuredin accordance with one or more aspects of the invention for enhancingimplantability and prolonged usage once implanted. However, furtherembodiments of the invention may be implemented as external infusiondevices, which connect to patients through suitable catheter devices orthe like. Yet further embodiments of the invention may be used in othercontexts, for delivery of a medium into other suitable environments.Therefore, for purposes of simplifying the present disclosure, the term“patient” is used herein to refer to the entity or environment in whichan implantable device is implanted or to which an external device isconnected, whether or not the implant or connection is carried out formedical purposes. Also, the term “infusion medium” is used herein torefer to any suitable medium delivered by the drive device.

The device 10 includes a generally disc-shaped housing 12. While agenerally circular disc-shaped embodiment is illustrated in FIG. 1, itwill be understood that further embodiments of the invention may employhousings of other shapes, including, but not limited to, oval, oblong,rectangular, or other curved or polygonal shapes. The housing 12 has adiameter dimension D, defining the diameter of the disc shape, and amaximum thickness dimension T, defining the maximum thickness of thedevice. In implantable device embodiments, the housing 12 is made of abiocompatible material and preferably has a relatively small orminimized thickness dimension T, to reduce or minimize patient traumaduring implant surgery and after implantation.

The housing 12 includes a reservoir housing portion 13 containing areservoir for holding a volume of infusion medium, such as, but notlimited to, a liquid medication to be administered to the patient. Thehousing 12 includes a further housing portion 14, located above thereservoir housing portion 13 in the orientation shown in FIG. 1, forcontaining a drive mechanism, a power source and control electronicsdescribed below.

Representative examples of reservoir housing portions and reservoirswhich may be employed in embodiments of the invention are described inco-pending U.S. patent application Ser. No. 60/317,880, titled “InfusionDevice And Reservoir For Same,” which is incorporated herein byreference. However, further embodiments may employ other suitablereservoir configurations, including, but not limited to, those describedin U.S. Pat. No. 5,514,103 and U.S. Pat. No. 5,176,644, each toSrisathapat et al, U.S. Pat. No. 5,167,633 to Mann et al., U.S. Pat. No.4,697,622 to Swift and U.S. Pat. No. 4,573,994 to Fischell et al.

The housing 12 also has an outlet 16 through which the infusion mediummay be expelled. When the device 10 is implanted in a patient orconnected externally to a patient, a catheter may be connected to theoutlet 16, to deliver infusion medium expelled from the outlet 16 intothe patient's blood stream or to a selected location in the patient'sbody. The infusion device 10 also includes an inlet structure 18 whichprovides a closeable and sealable fluid flow path to the reservoir inthe reservoir portion 13 of the housing. The inlet structure provides aport for receiving a needle through which fluid may be transferred tothe infusion device, for example, to fill or re-fill the reservoir ofthe device. In preferred embodiments, the inlet structure is configuredto re-seal after a fill or re-fill operation, and to allow multiplere-fill and re-seal operations. One example of an inlet structure isdescribed in co-pending U.S. patent application Ser. No. 60/318,056,titled “Infusion Device And Inlet For Same,” which is incorporatedherein by reference. However, further embodiments may employ othersuitable inlet structures, including, but not limited to, thosedescribed in U.S. Pat. No. 5,514,103 and U.S. Pat. No. 5,176,644, eachto Srisathapat et al, U.S. Pat. No. 5,167,633 to Mann et al., U.S. Pat.No. 4,697,622 to Swift and U.S. Pat. No. 4,573,994 to Fischell et al.

The infusion device 10 includes a drive mechanism 20, such as a pump,and an electronic control system 22 located in the housing portion 14.The drive mechanism 20 is connected between the reservoir and the outlet16. The electronic control system 22 includes a power source, such as abattery, and control electronics for controlling the drive mechanism 20to deliver infusion medium from the reservoir, to the patient in aselected manner. The drive mechanism may be controlled to deliverinfusion medium in any suitable manner, for example, according to aprogrammed dispensing rate or schedule or according to an actuationsignal from a sensor, timer or other suitable source.

In implantable embodiments, the portion 14 of the housing 12 thatcontains the drive mechanism 20 and control electronics 22 is preferablyhermetically sealed from the external environment and from the reservoirhousing portion 13, while the reservoir housing portion 13 may or maynot be hermetically sealed. In preferred embodiments, both the portion14 of the housing 12 and the reservoir housing portion 13 arehermetically sealed. In such an embodiment, the housing portion 14containing the drive mechanism 20 and control electronics 22 may be madefrom titanium or titanium alloy or other biocompatible metals, while thereservoir portion 13 of the housing may be made from such metals or abiocompatible and infusion medium compatible plastic.

The drive mechanism 20 includes mechanical and electromagneticcomponents that inherently inhabit a volume of space within the housingportion 14 in which the components reside and operate. In that regard,the drive mechanism 20 can contribute to the thickness requirements ofthe housing portion 14 and, thus, to the overall thickness dimension Tof the device 10. Preferred embodiments of the present invention relateto and employ drive mechanism configurations that reduce or minimize thethickness requirements of the device, without compromising drivecapabilities.

The ability to reduce or minimize the device thickness dimension T,without compromising the drive capabilities, can provide significantadvantages with respect to patient comfort, appearance and flexibilityin selecting implant locations in the body. Accordingly, drive mechanismconfigurations that allow for reduced or minimized device thicknessdimensions, as described herein, can provide significant advantages inthe implantable infusion device technology. Thus, in preferredembodiments, the drive mechanism 20 is configured with one or morefeatures described herein that provide a relatively small or minimalthickness and allow the device 10 to have a relative small or minimalthickness T.

Also in preferred embodiments, the device 10 is configured such that,once implanted, it functions for a relatively long period of time toadminister infusion medium to the patient and periodically bereplenished from outside of the patient's body. The operational life ofthe device 10 is, however, limited in part by the capacity of its powersource and the power requirements of the device. Preferred embodimentsof the device 10 employ drive mechanisms, as described below, thatprovide reliable pumping action and are highly efficient with respect topower consumption, to improve the operational life of the device 10.Alternatively or in addition, drive mechanisms that provide highlyefficient use of power, as described below, may be operated with smallerpower sources (for example, smaller batteries) which can allow thedevice 10 to be made smaller.

One manner of lowering the power consumption requirements of the device10 is to employ a coaxial coil and piston pump configuration and one ormore features described herein for making highly efficient use ofelectromagnetic energy. Another manner of lowering the power consumptionrequirements of the device 10 is to reduce the number of operations ofthe drive mechanism 20 required over a given period of time, by pumpingreduced volumes of a higher concentration infusion medium (an infusionmedium with a higher concentration of active ingredients) or pumpinghigher concentration volumes at reduced intervals. However, higherconcentration mediums may require a greater precision in controlling thevolume delivered to the patient during a drive operation, to avoiddelivering too great or too small of a volume of the higherconcentration medium to the patient. Accordingly further preferred drivemechanisms 20 are configured with one or more features described hereinto allow delivery of controlled volumes of infusion medium and, thus, toallow sufficiently precise delivery of relatively high concentrationinfusion medium.

First Drive Mechanism Embodiment

FIG. 2 shows a drive mechanism 20 according to one example embodiment ofthe present invention. In the illustrated embodiment, the drivemechanism 20 has a partially cylindrical, disc-shaped configuration withextended corners 24 and 25. An inlet 27 is provided at the corner 24 andan outlet 28 is provided at the corner 25. The inlet 27 may be connectedin flow communication with the reservoir portion 13 of the device 10 inFIG. 1, though suitable conduit (not shown) within the device 10.Similarly, the outlet 28 may be connected in flow communication with theoutlet 16 of the device 10 in FIG. 1, through suitable conduit (notshown) within the device 10.

FIG. 3 shows a cross-sectional view of an embodiment of a drivemechanism 20, in a retracted position or state. FIG. 4 shows across-sectional view of the same drive mechanism 20 embodiment, in aforward position or state. As described in more detail below, the drivemechanism 20 employs electromagnetic and mechanical forces to change (ormove) between retracted and forward states, to cause infusion medium tobe drawn in through the inlet 27 and forced out of the outlet 28. Thedrive mechanism 20, according to one embodiment, comprises an assemblyof components as shown in an exploded view in FIG. 5. Some of thesecomponents are also shown in perspective views in FIGS. 6–10.

With reference to those drawings, the drive mechanism 20 includes ahousing member 30 that is open on one side to a hollow, annular interiorsection 31. FIGS. 6 and 7 show two perspective views of the housing 30.The housing member 30 has a central hub portion 34 with a central pistonchannel 35. The bottom side of the housing member 30 (with reference tothe orientation shown in FIGS. 3 and 4), includes an opening to thehollow interior section 31 through which coil wires may pass, asdescribed below. The bottom side of the housing member also includes aconfiguration of recesses and cavities for providing an outlet chamber,an outlet passage and, in some embodiments, accumulator chambers asdescribed below. The housing member 30 is preferably made of a generallyrigid, biocompatible and infusion medium compatible material, having noor low magnetic permeability such as, but not limited to, titanium,stainless steel (which may be ferritic or non-ferritic), biocompatibleplastic, ceramic, glass or the like.

As shown in FIGS. 3 and 4, a coil cup 32 is located within the annularinterior section of the housing 30. A perspective view of the coil cup32 is shown in FIG. 8. The coil cup 32 has a generally cylinder shape,open on one side to a hollow, annular interior 33. The coil cup includesan open piston channel or bore 36 located in a central hub portion 37,axial relative to the annular interior. The hub portion 37 of the cupmember defines an inner annular wall 90 having an end surface 91 (orinner pole surface) of width W₁. The cup member has an outer wall 92having an end surface 93 (or outer pole surface) of a width W₂. Theouter wall 92 is connected to the inner wall 90 or hub portion 37 by abackiron portion of the cup member. As described in further detailbelow, at the open end of the cup member, the end surfaces 91 and 93 ofthe inner and outer walls 90 and 92 define pole surfaces that cooperatewith pole surfaces on an armature to provide a path for electromagneticflux during a forward stroke of the drive mechanism. In preferredembodiments, the width W₁ of inner pole surface 91 is greater than thewidth W₂ of the outer pole surface 93, to provide certainelectromagnetic characteristics as described below.

When assembled, the coil cup is located in the hollow interior of thehousing member 30, with the central portion 34 of the housing 30extending through the piston channel 36 of the coil cup 32, as shown inFIGS. 3 and 4. A coil 38 is located within the hollow, annular interiorof the coil cup 32, and is disposed around the axis A of the annularinterior of the coil cup 32. The coil cup 32 is provided with an opening84, through which coil leads extend, as shown in FIGS. 3 and 4. The coilcup 32 is preferably made of a generally rigid material, having arelatively high magnetic permeability such as, but not limited to, lowcarbon steel, iron, nickle, ferritic stainless steel, ferrite, otherferrous materials, or the like. The coil 38 comprises a conductive wirewound in a coil configuration. The coil wire may comprise any suitableconductive material such as, but not limited to, silver, copper, gold orthe like, with each turn electrically insulated from adjacent turns andthe housing. In one preferred embodiment, the coil wire has a square orrectangular cross-section, to allow minimal space between windings,thereby to allow a greater number of coil turns and, thus, improvedelectrical efficiency.

The drive mechanism 20 also includes an actuator member 40, which has anarmature portion 42 and a piston portion 44. The actuator member ispreferably made of a generally rigid, biocompatible and infusion mediumcompatible material, having a relatively high magnetic permeability suchas, but not limited to, ferrous materials, ferritic stainless steel withhigh corrosion resistance, or the like. In the embodiment of FIGS. 3, 4and 9, the actuator (with an armature portion 42 and a piston portion44) is formed as a single, unitary structure. In other embodiments asdescribed below, the piston portion may be a separate structure withrespect to the armature portion.

A perspective view of an example actuator member 40 is shown in FIG. 9,wherein the armature portion 42 of the actuator member has a round, discshape, provided with at least one opening and, preferably, a pluralityof openings as shown in the drawing. The openings in the illustratedexample include a plurality of larger openings 41 which are elongated inthe radial dimension of the armature, and a plurality of smalleropenings 43, each disposed between a pair of larger openings 41. Thesections 45 of the armature 42 between the openings 41 and 43 defineradial struts coupling an annular outer section (or outer pole) 47 to aninner section (or inner pole) 49 of the armature. In preferredembodiments, the width W₁ of the inner pole surface 49 is greater thanthe width W₂ of the outer pole surface 47, corresponding to thedifference between the width of the pole surface 91 on the inner wall 90of the cup member and the width of the pole surface 93 on the outer wall92 of the cup member.

As described in more detail below, the armature 42 cooperates with theinner and outer walls of the coil cup 32, to provide a flux path forelectromagnetic flux. The spacing between the pole surfaces on thearmature 42 and the pole surfaces on the coil cup walls define gaps inthe flux path. In preferred embodiments, the spacing between the outerpole surface 47 of the armature 42 and the outer pole surface 93 of theouter wall 92 of the coil cup 32 (or the barrier 48) is greater than thespacing between the inner pole surface 49 of the armature and the polesurface 91 of the inner wall 90 of the coil cup (or the barrier 48),when the actuator is in the retracted position shown in FIG. 3. Agreater outer pole spacing, relative to the inner pole spacing, canresult in reduced residual flux that could otherwise cause the armatureto stick in the forward position (the FIG. 4 position). In addition, agreater outer pole spacing reduces the squeezing effect on infusionmedium between the outer pole of the armature 42 and the barrier 48, asthe armature 42 moves toward the forward position during actuation ofthe pump mechanism.

The radial struts 45 in the armature provide radial paths forelectromagnetic flux between the outer and inner pole sections 47 and 49of the armature. The openings 41 and 43 provide a passage for infusionmedium to pass, as the actuator 40 is moved between retracted andforward stroke positions, to reduce resistance to the actuator motionthat the infusion medium may otherwise produce. In the embodimentillustrated in FIG. 9, additional openings are provided around thepiston portion 44, to provide additional flow paths for infusion mediumto pass. The configuration of openings is preferably designed to providea sufficient conductor for electromagnetic flux and, yet minimize orreduce viscous resistance to actuator motion. To further reduce viscousresistance during actuator motion in the forward stroke direction, theinner and outer pole sections 47 and 49 may have textured surfacesfacing the coil cup 38, to provide flow areas for medium between thepole sections 47, 49 and the coil cup 38 (or barrier 48 describedbelow).

With reference to FIGS. 3 and 4, the actuator member 40 is arranged withthe piston portion 44 extending through the axial channel 35 of thehousing 30 and with the armature portion 42 positioned adjacent the openside of the coil cup 32. An actuator spring 46 is positioned to forcethe armature portion 42 of the actuator 40 in the direction away fromthe open side of the coil cup 32, to provide a gap between the armature42 and the open side of the coil cup 32. A biocompatible and infusionmedium compatible barrier 48 is located over the open side of the coilcup 32, between the armature 42 and the coil cup 32, to maintain a gapbetween those two members and/or to help seal the annular interior ofthe coil cup and coil 38. In other embodiments in which infusion mediummay contact the coil, the barrier 48 may be omitted.

The actuator spring 46 in the illustrated embodiment comprises a coilspring disposed around the piston portion 44 of the actuator 40,adjacent the armature portion 42. One end of the coil spring abuts thearmature portion 42 of the actuator, while the opposite end of the coilspring abuts a shoulder 39 in the piston channel 35 of the housing 30.In this manner, the actuator spring 46 imparts a spring force betweenthe housing and the actuator 40, to urge the actuator toward itsretracted position shown in FIG. 3.

In the illustrated embodiment, by using a coil spring 46 located aroundand coaxial with the piston portion 44 and disposed partially within thepiston channel 35, the actuator spring may have minimal or nocontribution to the overall thickness dimension of the drive mechanism.However, in other embodiments, actuator springs may have other suitableforms and may be located in other positions suitable for urging theactuator toward its retracted position shown in FIG. 3. The actuatorspring 46 is preferably made of a biocompatible and infusion mediumcompatible material that exhibits a suitable spring force such as, butnot limited to, titanium, stainless steel, MP35N cobalt steel or thelike.

The drive mechanism 20 further includes a cover member 50 which attachesto the housing member 30, over the open side of the housing member andthe barrier 48. The cover member 50 is preferably made of a generallyrigid, biocompatible and infusion medium compatible material, having arelatively low magnetic permeability (being relatively magneticallyopaque) such as, but not limited to, titanium, stainless steel,biocompatible plastic, ceramic, glass or the like.

The cover member 50 defines an interior volume 51 between the barrier 48and the inner surface of the cover member. The armature portion 42 ofthe actuator member 40 resides within the interior volume 51 when thecover is attached to the housing, as shown in FIGS. 3 and 4. Asdescribed below, the armature 42 is moveable in the axial direction Awithin the volume 51, between a retracted position shown in FIG. 3 and aforward stroke position shown in FIG. 4. This movement is created by theaction of electromagnetic force generated when a current is passedthrough the coil 38 and the mechanical return action of the actuatorspring 46.

An adjusting plunger 52 is located within the cover 50, for contactingthe armature 42 when the armature is in the fully retracted positionshown in FIG. 3, to set the retracted or retracted position of thearmature. In preferred embodiments, a seal may be disposed between theplunger 52 and the cover member 50, for example, but not limited to, asilicon rubber sealing ring. In further embodiments, a flexiblediaphragm 59 (such as, but not limited to, a thin titanium sheet orfoil) may be coupled to the inside surface of the cover 50 and sealedaround the opening through which the plunger 52 extends. The diaphragmwill flex to allow the plunger to define an adjustable retractedposition and, yet, provide sealing functions for inhibiting leakage atthe interface between the plunger 52 and the cover 50. In furtherpreferred embodiments, once a proper armature position is set, theplunger is fixed in place with respect to the cover member, for example,by adhering the plunger to the cover member with one or more welds,adhesives or other securing methods.

The cover member 50 includes the inlet 27 of the drive mechanism, whichhas an inlet opening 54 in fluid flow communication with the interiorvolume 51, as described below. The inlet opening 54 connects in fluidflow communication with the reservoir of the infusion device 10 (FIG.1), to receive infusion medium from the reservoir. Connection of theinlet opening 54 and the reservoir may be through suitable conduit (notshown), such as tubing made of suitable infusion medium compatiblematerial, including, but not limited to titaniaum, stainless steel,biocompatible plasitc, ceramic, glass or the like.

The inlet opening 54 provides a flow path to an inlet chamber 56 formedin the cover member 50, adjacent the inlet opening. A filter or screenmember, such as a porous or screen material 58, may be disposed withinthe inlet chamber 56. The filter or screen member 58 is provided in aflow path between the inlet opening 54 and an inlet port 60 to thevolume 51. A one-way inlet valve (not shown), to allow medium to flowinto but not out of the interior volume 51 through the inlet, may alsobe provided in the flow path between the inlet opening 54 and the inletport 60, or within the inlet port 60. The cover member 50 may beprovided with an inlet cover 62 that, when removed, allows access to theinlet chamber 56 to, for example, install, replace or service a filter58 or inlet valve, or to service or clean the inlet 27. However, in onepreferred embodiment, an inlet valve is omitted and, instead, the drivemechanism 20 is configured as a single valve mechanism, employing asingle outlet valve (for example, outlet valve assembly 67 describedbelow) and no inlet valve.

As shown in FIGS. 3 and 4, the piston portion 44 of the actuator 40extends through the axial channel 35 in the housing 30, toward an outletchamber 64 at the end of the axial channel 35. The channel 35 has aninside diameter which is larger than the outside diameter of the pistonportion 44. As a result, an annular volume is defined between the pistonportion 44 and the wall of the axial channel 35, along the length of theaxial channel 35. Infusion medium may flow through the annular volume,from the volume 51 within the cover 50 to a piston chamber 65 locatedbetween the free end of the piston portion 44 and a valve member 66 of avalve assembly 67. In preferred embodiments, the radial spacing betweenthe piston portion 44 and the wall of the channel 35 is selected to belarge enough to provide a suitable flow toward the piston chamber 65 torefill the piston chamber 65 (during a return stroke of the pistonportion), but small enough to sufficiently inhibit back flow of mediumfrom the piston chamber 65 (during a forward stroke of the pistonportion).

The actual radial spacing between the piston portion 44 and the wall ofthe channel 35 to achieve such results depends, in part, on the overalldimensions of those components, the pressure differentials created inthe mechanism and the viscosity of the infusion medium. In preferredembodiments, the radial spacing is selected such that the volume ofmedium for refilling is between about 1 and 4 orders of magnitude (and,more preferably, about 2 orders of magnitude) greater than the volume ofmedium that backflows through the space. Alternatively, or in addition,the radial spacing may be defined by the ratio of the diameter D_(P) ofthe piston portion 44 the diameter D_(C) of the channel 35, where theratio D_(P)/D_(C) is preferably within a range of about 0.990 to about0.995. As a representative example, a total spacing of about 400 to 600micro-inches and, preferably, an average radial gap of about 250micro-inches annularly around the piston portion 44 may be employed.

The valve assembly 67 in the embodiment of FIGS. 3 and 4 includes thevalve member 66, a valve spring 68 and support ring 70. The valve member66 is located within the outlet chamber 64 and, as shown in FIG. 3, ispositioned to close the opening between the axial channel 35 and theoutlet chamber 64, when the actuator 40 is in the retracted position. InFIG. 4, the valve member 66 is positioned to open a flow passage betweenthe axial channel 35 and the outlet chamber 64. The valve spring 68 islocated within the outlet chamber 64, to support the valve member 66.The spring 68 imparts a spring force on the valve member 66, in thedirection toward piston 44, urging the valve member 66 toward a closedposition, to block the opening between the axial channel 35 and theoutlet chamber 64.

The valve member 66 is preferably made of a generally rigid,biocompatible and infusion medium compatible material, such as, but notlimited to, titanium, stainless steel, biocompatible plastic, ceramic,glass, gold, platinum or the like. A layer of silicon rubber or othersuitable material may be attached to the rigid valve member material, onthe surface facing the channel 35, to help seal the opening to thechannel 35 when the valve member is in the closed position shown in FIG.3.

The valve spring 68 is preferably made of a biocompatible and infusionmedium compatible material that exhibits a suitable spring force suchas, but not limited to, titanium, stainless steel, MP35N cobalt steel orthe like. In the illustrated embodiment, the valve spring 68 has agenerally flat, radial or spiral configuration. In preferredembodiments, the spring 68 includes radial arms that contact theinterior of the outlet chamber in multiple locations around theperiphery of the spring, to inhibit lateral or radial motion and improvestability of the spring. In further embodiments, a conical or bellevillespring may be used. In yet further embodiments, other suitable valvespring configurations may be employed, including, but not limited tohelical, conical, barrel, hourglass, constant or variable pitch springsor the like.

In the embodiment of FIGS. 3 and 4, the valve spring 68 is spaced from avalve cover 72 by the ring 70. The valve cover 72 is sealed to thehousing 30, to enclose the outlet chamber 64. The ring 70 is disposedwithin the outlet chamber 64, between the spring 68 and the valve cover72. With the valve member 66 supported between the spring 68 and theopening to the channel 35, the force imparted by the spring on the valvemember is dependent, in part, on the characteristics and parameters ofthe spring and, in part, on the position of the spring within the outletchamber. The ring 70 and the valve cover 72 are each preferably made ofa generally rigid, biocompatible and infusion medium compatiblematerial, such as, but not limited to, titanium, stainless steel,biocompatible plastic, ceramic, glass, gold, platinum or the like.

The thickness dimension T_(R) of the ring 70 may be matched to fitwithin a recess within the outlet chamber, as shown in FIGS. 3 and 4.Alternatively, the thickness dimension T_(R) of the ring 70 may beselected to define the position of the spring 68 within the outletchamber, by defining the distance of the spring 68 relative to the valvecover 72 and relative to the opening between the axial channel 35 andthe outlet chamber 64. A larger ring thickness T_(R) will space thespring further from the valve cover 72 and closer to the opening to theaxial channel 35, while a smaller ring thickness T_(R) will space thespring closer to the valve cover 72 and further from the opening to theaxial channel 35. In this manner, for a given spring 68, the forceimparted by the spring on the valve member 66 to close the opening tothe axial channel 35 (as shown in FIG. 3) may be selected or adjusted byselecting or adjusting the ring thickness T_(R). The ring thicknessT_(R) and the spring characteristics are preferably selected to providesufficient force to urge the valve member 66 into a suitably sealed orclosed position as shown in FIG. 3, yet allow the movement force of thepiston portion 44 (caused by electromagnetic force generated by thecoil) to overcome the spring force and open the valve member 66 as shownin FIG. 4.

In the illustrated embodiment, the outlet chamber 64 comprises a cavityin the bottom of the housing 30, as shown in FIGS. 3, 4 and 7. Thus, inthe illustrated embodiment, the outlet chamber cavity is generallycentered within the same housing 30 that has the cavity holding the coilcup 32 and coil 38. With such an arrangement, the configuration of thedrive mechanism 20 may be made with a relatively small thicknessdimension (height dimension in the orientation shown in FIGS. 3 and 4)without compromising structural strength, as compared to alternativeconfigurations in which the outlet chamber is formed with a separatemember coupled to the housing 30.

As shown in FIG. 7, the outlet chamber cavity 64 may be provided in flowcommunication with an outlet 28 through a flow passage 74 and one ormore accumulator cavities 78. The flow passage 74 comprises a channelwhich leads to the outlet 28 of the drive mechanism 20 and, eventually,to the device outlet 16 (FIG. 1). The outlet chamber cavity 64, flowpassage 76, accumulator cavities 78 and flow passage 74 provide a flowpath for infusion medium to flow from the outlet chamber to the deviceoutlet 16, under pressure induced by operation of the drive mechanism20. As shown in FIG. 7, the accumulator cavities 78, flow passage 76 andflow passage 74 may be provided lateral to the outlet chamber cavity 64in the housing 30 to, thus, have minimal or no additional contributionto the overall thickness dimension T of the drive mechanism than thatalready required by the outlet chamber cavity 64.

Each accumulator cavity 78 forms a chamber which may contain one or moreflexible, sealed packets, or accumulators, containing a compressiblemedium. In one preferred embodiment, each accumulator preferablycomprises a packet made of a biocompatible and infusion mediumcompatible material of sufficient strength and flexibility to compressand expand under varying fluid pressures, such as, but not limited tostainless steel, titanium, platinum, which contains a compressiblemedium, such as, but not limited to a noble gas, such as argon or neon,or other suitable materials and media that provide a return pressureover a broad range of compression pressures. The accumulators may beused to help stabilize the flow rate of the drive mechanism and providea relatively constant output pressure during drive operations, by actingas damping structures within the flow path between the outlet chamber 64and the outlet 28. In addition, the accumulators may minimize backflowdown axial channel 35 while the valve is closing or even prior to thevavle closing.

For example, as shown in FIG. 10, one or more disc-shaped accumulators80 may be stacked within each accumulator cavity, with or without anadditional volume 82 for infusion medium. As the pressure of theinfusion medium within the accumulator cavity increases, theaccumulators 80 compress to increase the volume 82. Similarly, as theinfusion medium pressure decreases, the accumulators 80 may expand anddecrease the volume 82. In this manner, the accumulators 80 inhibitsharp changes in infusion medium pressure and provide a dampeningmechanism for dampening pressure changes to allow a relatively constantpressure flow through the outlet 28, during operation of the drivemechanism 20. While the illustrated embodiment employs two accumulatorcavities, each having two accumulators, other embodiments may employ anysuitable number of accumulator cavities and accumulators. Otherembodiments may employ cavities 78, without accumulators or with othermechanisms that provide volume adjustment or flow smoothingcapabilities, including, but not limited to, bellows structures,sponge-type structures, fluid accumulators or the like Yet otherembodiments, in which the maintenance of a relatively constant outletpressure is not a concern, may omit accumulator cavities andaccumulators, such that the outlet chamber is directly coupled to theoutlet port.

A drive mechanism as shown in FIGS. 3 and 4 may be constructed byproviding components as shown in FIG. 5 and assembling the components inany suitable sequence. The components may be made according to anysuitable process including, but not limited to molding, machining,extruding, sintering, casting, combinations thereof or the like.

The coil 38 may be inserted into the annular interior 33 of the coil cup32, with the coil leads extended through a coil lead opening 84 in thecoil cup. The coil may be impregnated or partially impregnated with afill material of epoxy or the like, for adhering the coil to the coilcup and for sealing or partially sealing the coil. The fill material mayalso be used to adhere the barrier plate to the coil members, to avoidwarping or bulging of the barrier plate after assembly.

The coil cup 32 and coil 38 may be inserted into the interior 31 of thehousing 30, with the coil leads (which may be wire leads or flexibleconductive tabs) extending through a coil lead opening 86 in the housing30. In preferred embodiments, the coil cup and housing are configured toprovide a tight, friction fit therebetween, without requiring additionalmeans of adhering the two components together. In other embodiments, thecoil cup 32 and housing 30 may be coupled together by any suitableadhesive material or other adhering methods, including, but not limitedto welding, brazing, of the like.

The barrier 48 may be placed over the coil, coil cup and housingsub-assembly. The barrier 48 may be adhered to the housing by one ormore adhering points or continuously along the circumference of thebarrier 48, with any suitable adhesive material or other adheringmethods, including, but not limited to welding, brazing, soldering orthe like. Alternatively, or in addition, the barrier 48 may be held inplace by a shoulder portion of the cover 50, as shown in FIGS. 3 and 4.In addition, as noted above, the barrier 48 may be adhered to the coil38 by fill material in the coil. In preferred embodiments, the barrier48 is held in a generally flat relation relative to the coil cup andcoil. To enhance this flat relation, the coil cup and housing mayassembled together and then machined to planarize the barrier contactsurfaces, prior to inserting the coil in the coil cup and prior toadding fill material to the coil.

Once the barrier 48 is placed over the coil, coil cup and housing, theactuator 40 may be added to the sub-assembly. First, however, theactuator spring 46 is placed around the piston portion 44, adjacent thearmature portion 42 of the actuator. Then the free end of the pistonportion 44 is passed through the axial channel 35 of the housing 30,with the armature end of the actuator arranged adjacent the barrier 48.

The cover member 50 may then be disposed over the armature end of theactuator and secured to the housing 30. In preferred embodiments, thecover member 50 is adhered to the housing by one or more adhering pointsor continuously along the circumference of the cover member 50, with oneor more welds or any other suitable adhering methods, including, but notlimited to adhesive materials, brazing or the like. The inlet filter 58and inlet cover 62 may be pre-assembled with the cover member 50, priorto adding the cover member to the sub-assembly. Alternatively, thefilter 58 and inlet cover 62 may be added to the cover member 50 afterthe cover member 50 is assembled onto the housing 30. In preferredembodiments, the filter 58 is disposed within the inlet chamber 56 and,then, the inlet cover 62 is adhered to the cover member 50 by one ormore adhering points or continuously along the circumference of theinlet cover, with one or more welds or any other suitable adheringmethods, including, but not limited to adhesive materials, brazing orthe like.

The valve side of the drive mechanism may be assembled before or afterthe above-described components are assembled. On the valve side of thedrive mechanism, the valve member 66 is disposed within the outletchamber cavity 64 of the housing 30, adjacent the opening to the axialchannel 35. The valve spring 68 is then disposed within the outletchamber cavity 64, adjacent the valve member 66. The ring 70 is thendisposed in the cavity 64, adjacent the spring 68. Any suitable numberof accumulators may be placed within each of the accumulator cavities78. The valve cover 72 may then be placed over the outlet chamber cavity64 and accumulator cavities 78. In preferred embodiments, the housing 30is provided with a recess 88 around the periphery of the cavities thatform the outlet chamber cavity 64, accumulator cavities 78, outlet port74 and flow passage 76, for providing a seat for the valve cover 72. Inthis manner, the valve cover 72 fits within the recess 88, flush withthe housing 30. Also in preferred embodiments, the valve cover 72 isadhered to the housing 30 by one or more adhering points or continuouslyalong the circumference of the valve cover, with one or more welds orany other suitable adhering methods, including, but not limited toadhesive materials, brazing or the like.

The volume of the piston chamber 65, the compression of the actuatorspring 46 and the position of the actuator 40 in the retracted positionshown in FIG. 3 may be adjusted by the adjusting the position of theadjusting plunger 52. In one preferred embodiment, the adjusting plungerincludes a threaded cylindrical member, which engages correspondingthreads in a plunger aperture in the cover member 50, to allowadjustment in a screw-threading manner. The diaphragm 59 under theplunger 52 contacts the armature portion 42 of the actuator, inside ofthe cover member 50. The other end of the plunger 52 may be providedwith a tool-engagement depression, for allowing engagement by a tool,such as a screw-driver, Allen wrench or the like, from outside of thecover member 50. By engaging and rotating the plunger 52 with a suitabletool, the depth that the plunger extends into the cover member 50 may beadjusted, to adjust the retracted position of the armature portion 42relative to the barrier 48 (to adjust the gaps between the pole sections47, 49 of the armature and pole sections formed by the coil cup 32, whenthe actuator is in the retracted position of FIG. 3). In one preferredembodiment, adjustments of the plunger 52 are made during manufacture.In that embodiment, the adjusted position is determined and set bywelding or otherwise adhering the plunger 52 in the adjusted positionduring manufacture. In other embodiments, the plunger 52 is not set andwelded during manufacuture, to allow adjustment of plunger 52 aftermanufacture.

The resulting drive mechanism 20 may, therefore, be constructed toprovide a relatively thin form factor and, yet provide a reliableoperation that can deliver a relatively constant flow pressure andrelatively precise volumes of infusion medium. A number of features canprovide, or be combined to contribute to, reductions in the thicknessform factor of the drive mechanism. For example, the coaxial arrangementof components such as the piston portion 44 and the coil 38, with a flowchannel formed within the piston channel 35, can be implemented with asmaller thickness form factor (in the vertical dimension of FIGS. 3 and4) than alternative arrangements in which those components are arrangedadjacent each other in the thickness dimension.

Furthermore, the arrangement of an inlet volume 51 on one side of thecoil 38 and an outlet chamber 64 on the opposite side of the coil 38,with a flow passage through the channel 35 in the coil 38 can alsocontribute to a reduction in the required thickness dimension of thedrive mechanism, by allowing the coil 38 and channel 35 to share acommon portion of the thickness dimension. The arrangement of thearmature portion 42 to move within the inlet volume 51 allows thosefeatures to share a common portion of the thickness dimension. Thearrangement of the outlet chamber 64 in a central location within thesame housing that has the coil cup cavity allows those features to beformed in relatively close proximity to each other in the thicknessdimension. The arrangement of the outlet chamber, outlet port andaccumulator cavities in the housing 30 allows those features to share acommon portion of the thickness dimension of the drive mechanism.Further features, including recessed shoulders 39 for the actuatorspring 46, the use of a relatively flat valve spring 68 and generalattention to minimizing thickness dimensions of components, wherepossible, can also contribute to reductions in the overall thicknessdimension of the drive mechanism.

In addition, a number of features described herein can provide, or becombined to contribute to, the efficient use of power to, prolong theoperational life of the drive mechanism. For example, a reduction inleakage of electromagnetic flux during coil energization, and, thus, amore efficient use of the flux generated by the coil, may be provided byconfiguring the width W₁of the pole surface on the inner wall 90 of thecup member wider than the width W₂ of the pole surface on the outer wall92 of the cup member. Similarly, more efficient conduction ofelectromagnetic flux may be provided by an actuator configured with awider inner pole surface 49 than its outer pole surface 47. Also, moreefficient conduction of electromagnetic flux may be provided by anactuator configured with radial sections 45 connecting the annular innerand outer pole surfaces 49 and 47.

Operation of First Drive Mechanism Embodiment

In operation, the drive mechanism 20 employs electromagnetic andmechanical forces to move between retracted (FIG. 3) and forward (FIG.4) positions, to cause infusion medium to be drawn into and driven outof the mechanism in a controlled manner. In the retracted position, thespring 46 urges the actuator 40 toward its retracted position shown inFIG. 3. When the coil 38 is energized to overcome the spring force ofspring 46, the actuator 40 moves to its forward stroke position shown inFIG. 4. The movement of the actuator between retracted and forwardpositions creates pressure differentials within the internal chambersand volumes of the drive mechanism 20 to draw medium into the inlet 27and drive medium out the outlet 28.

More specifically, when the coil 38 is de-activated (not energized ornot energized in a manner to overcome the spring force of spring 46),the actuator 40 is held in its retracted position (FIG. 3) under theforce of the spring 46. When the coil is deactivated immediatelyfollowing a forward stroke, the spring 46 moves the actuator 40 to theretracted position of FIG. 3, from the forward position shown in FIG. 4.The openings 41 and 43 in the armature portion 42 of the actuator 40provide passages for medium to pass and, thus, reduce viscous drag onthe actuator. As a result, the actuator 40 may move to its retractedposition (FIG. 3) relatively quickly.

As the actuator 40 retracts, the piston portion 44 of the actuator isretracted relative to the valve member 66, such that a piston chamber 65volume is formed between the end of the piston portion 44 and the valvemember 66. The formation of the piston chamber 65 volume creates anegative pressure which draws infusion medium from the volume 51 of thecover member 50, through the annular space between the piston portion 44and the wall of the channel 35, and into the piston chamber 65. Whilenot shown in FIG. 3, other embodiments (such as shown in FIGS. 11 and12) may include one or more channels through the piston portion 44, toprovide one or more additional flow paths to the piston chamber 65.

In the retracted position, a gap is formed between each of the annularpole surfaces 91 and 93 defined by the inner and outer walls 90 and 92of the coil cup 32 and a respective annular surfaces of the inner andouter pole sections 49 and 47 of the actuator's armature portion 42. Inparticular, with reference to FIG. 3, a first gap 94 is formed betweenthe annular pole surface 91 of the inner cup member wall 90 and theannular surface of the inner pole section 49. A second gap 95 is formedbetween the annular surface 93 of the outer cup member wall 92 and theannular surface of the outer pole section 47.

When the coil 38 is energized (or energized in a manner to overcome thespring force of spring 46), the actuator 40 is forced in the directionto close the gaps 94 and 95 and moves to its forward position (FIG. 4)under the influence of electromagnetic flux generated by the energizedcoil. In particular, the coil may be energized by passing an electricalcurrent through the coil conductor to create electromagnetic flux. Theelectromagnetic flux defines a flux path through the coil cup walls,across the gaps 94 and 95 and through the armature portion of theactuator. The electromagnetic flux provides an attraction force betweenthe annular surfaces 91, 93 of the coil cup 32 and the annular surfacesof the armature's pole sections 47, 49, to overcome the spring force ofspring 46 and draw the armature 42 toward the coil cup.

As the armature portion 42 of the actuator is drawn toward the coil cup32, the piston portion 44 of the actuator is moved axially through thechannel 35, in the direction toward the outlet chamber 64. With the coilenergized, the piston portion 44 continues to move under the action ofthe armature, until a mechanical stop is reached, for example,mechanical contact of the actuator 40 with the barrier 48, a portion ofthe housing 30 or cover member 50. In other embodiments, the motion maycontinue until the return force of the spring and fluid pressureovercomes the electromagnetic force provided by energizing the coil.

The movement of the piston portion 44 towards the stopping point reducesthe volume of the piston chamber 65 and increases the pressure withinthe piston chamber until the pressure is sufficient to overcome theforce of the valve spring 68. As the valve spring force is overcome bythe pressure within the piston chamber, the valve member 66 is movedtoward an open position, away from the opening between the pistonchamber 65 outlet chamber 64. When the valve member 66 is in the openposition, medium is discharged through the outlet chamber 64 and outlet28 (FIG. 7).

When the coil is deactivated and the piston portion 44 is moved back toits retracted position, the pressure in the piston chamber 65 reducesand the valve member 66 is reseated under the action of the valve spring68. This prevents fluid from flowing back into the drive mechanism,through the outlet. In addition, a negative pressure is created in thepiston chamber 65 to draw medium into the chamber for the next forwardstroke, as described above.

In this manner, energization of the coil 38 to move the actuator 40 toits forward position (FIG. 4) causes a measured volume of medium to bedischarged from the outlet. As described above, when the coil 38 isde-energized, the actuator 40 is returned to the retracted position(FIG. 3) under the force of spring 46 and an additional volume of mediumis drawn into the piston chamber 65 for the next discharging operation.Accordingly, the coil 38 may be energized and de-energized by acontrolled electronic pulse signal, where each pulse may actuate thedrive mechanism 20 to discharge a measured volume, or bolus, of medium.In preferred embodiments, the coil 38 may be electrically coupled to anelectronic control circuit (not shown) to receive an electronic pulsesignal from the control circuit for example, in response to a sensorsignal, timer signal or other control signal input to the controlcircuit.

In preferred embodiments, when the piston motion is stopped at the endof the forward stroke, the valve-facing end of the piston portion 44 isin close proximity to the valve member 66, for example, spaced from thevalve member 66 by no more than about ten percent (10%) of the pistondiameter. In further embodiments, the valve facing end of the pistonportion 44 is in contact with the valve member 66, at the end of theforward stroke. In this manner, gas that may be present in the infusionmedium is less likely to accumulate within the piston chamber 65. Morespecifically, in some operational contexts, infusion medium may containgas in the form of small bubbles that may migrate into the pistonchamber 65 during filling of the piston chamber. As gas is significantlymore compressible than liquid, too much gas within the piston chambermay adversely affect the ability of the drive mechanism to self prime.

In yet another embodiment the piston portion 44 may contact the valvemember 66 at the end of the forward stroke and push the valve member 66open. In this embodiment, it is less likely that gas will be trappedbetween the piston portion 44 and the valve member 66, and more likelythat the chamber will be purged of gas.

The total ullage is the sum of (1) the volume at the valve-facing end ofthe piston portion 44 in a forward position (FIG. 4) and (2) the volumeof the annular space between the piston portion 44 and the wall of thechannel 35. In preferred embodiments, to provide self-primingproperties, the total of those two volumes is selected to be about 25%of the volume of the volume 65.

When the actuator is stopped, for example, by contact with the barrier48 or other mechanical stop structure, the coil current/voltagerelationship-changes. In preferred embodiments, control electronics (notshown) are connected to detect the change in coil current or voltage anddeactivate the coil when the armature reaches the stop point. In thismanner, the coil may be energized for only as long as theelectromagnetic flux generated by the coil is providing useful work.Once the actuator motion is stopped and no further useful work isprovided by the electromagnetic flux, the coil may be deactivated toreduce or minimize power consumption requirements of the drivemechanism.

In addition, such control electronics may also adapt to altitude changesand further reduce or minimize power consumption of the drive mechanism.In particular, a differential pressure exists between the inlet and theoutlet ports of the drive mechanism during operation. The differentialpressure resists the motion of the actuator in the forward directionand, consequently, consumes energy. However, the differential pressuretends to reduce with increasing altitude, requiring less energy to movethe actuator. By deactivating the coil when the actuator stopping pointis sensed, the drive mechanism can, effectively, automatically adjust toaltitude changes and provide power consumption efficiency independent ofaltitude in which the drive mechanism is used. Conversley, the systemmay provide more power if there is a blocked catheter.

Further features described above may be employed for purposes ofimproving efficiency in power consumption, by more efficiently using theelectromagnetic flux generated by the coil during energization. Forexample, in preferred embodiments, the width of the first gap 94 (in thedimension from the surface 91 to the surfaces of the inner pole section49) is less than the width of the second gap 95 (in the dimension fromthe surface 93 to the surface of the outer pole section 47), when theactuator is in the retracted position. A greater outer pole spacing,relative to the inner pole spacing, can result in reduced residual fluxthat could otherwise cause the armature to stick in the forward position(the FIG. 4 position). In addition, a greater outer pole spacing reducesthe squeezing effect on infusion medium within the second gap, as thearmature 42 moves toward the forward position during actuation of thepump mechanism.

In further preferred embodiments, the width W₁ of the pole surface onthe inner wall 90 is greater than the width W₂ of the pole surface onthe outer wall 92 of the coil cup. In addition, the width W₁ of theinner pole surface 49 is greater than the width W₂ of the outer polesurface 47 of the armature, to correspond to the difference between thewidth of the inner wall 90 and the width of the outer wall 92 of the cupmember. In one preferred embodiment, the width of the outer pole surface47 of the armature is slightly larger than the width of the outer polesurface of the cup member wall 92 and the width of the inner polesurface 49 of the armature is slightly larger than the width of theinner pole surface of the cup member wall 90.

When the coil 38 is energized, the attraction force generated at the gapbetween a pair of pole surfaces is dependent upon the area of the polesurface. Forming the outer pole surfaces with a smaller width than theinner pole surfaces can compensate for the larger diameter and, thus,the larger surface area per unit of width of the outer pole surfacesrelative to the inner pole surfaces. In preferred embodiments, the widthof the pole surfaces are selected such that the attraction force at theinner pole is approximately 2.5 times the attraction force at the outerpole. This may be accomplished by configuring the width of the outerpole surface to have a surface area of approximately 2.5 times thesurface area of the inner pole surface.

Second Drive Mechanism Embodiment and Operation

A drive mechanism 120 according to a further embodiment of the inventionis shown, in cross-section, in FIGS. 11 and 12. In particular, FIG. 11shows the drive mechanism 120 in a retracted position, while FIG. 12shows the drive mechanism 120 in a forward position. Many aspects andfeatures of the mechanism 120 are similar to corresponding aspects andfeatures of drive mechanism 20 and for which reference is made to theabove description of drive mechanism 20. Other aspects and features ofdrive mechanism 120 that differ from drive mechanism 20 are apparentfrom the drawings and the description below.

The drive mechanism 120 may be employed in the device 10 of FIG. 1, in amanner similar to that described above with respect to drive mechanism20. Similar to the drive mechanism 20 of FIGS. 3 and 4, the drivemechanism 120 of FIGS. 11 and 12 includes an inlet 127, an outlet 128, ahousing 130, a coil cup 132, an axial channel 135, a coil 138, anarmature 142, a piston 144, a barrier member 148, a cover member 150having an interior volume 151, a valve member 166, an inlet port 160, anoutlet chamber 164, a piston chamber 165, a valve spring 168, a valvecover 172, and an outlet port 174. These features provide functions thatcorrespond to the functions of the corresponding features of drivemechanism 20 of FIGS. 3 and 4 (shown in FIGS. 3 and 4 with correspondingreference numbers, without the hundredth digit). Insofar as thesefeatures have structural and operational similarities reference is madeto the above descriptions of corresponding features, to avoidduplication of descriptions.

However, as noted above, various differences between the embodiments 20and 120 are apparent from the drawings. One difference relates to thearmature 142 and piston 144 which, together, form an actuator. In theembodiment of FIGS. 11 and 12, the armature and piston portions of theactuator are separate elements, while in the embodiment of FIGS. 3 and 4described above, the piston and armature are portions of a single,unitary actuator structure.

In addition, the piston 144 has a central flow passage 145 extendingbetween the two piston ends and open on each end to allow infusionmedium to flow through the piston and, thus, through the channel 135. Inthe illustrated embodiment, a single flow passage 145 is provided alongthe central axis of the piston 144. In other embodiments one or moreflow passages may be provided in a non-axial arrangement with or withoutan axial flow passage. With one or more central flow passages 145through the piston 144 to allow passage of infusion medium through thechannel 135, the spacing between the piston 144 and the wall of thechannel 135 may be relatively small. As a result, the speed of refillingof the piston chamber may be increased.

The armature 142 has openings 141, 143 through which infusion medium maypass. While not shown in FIGS. 11 and 12, the openings 141, 143 may bearranged to provide radial flux conduction paths on the armature, asdescribed above with respect to openings 41 and 43 in the armature 42 ofFIGS. 3 and 4. In addition, the armature 142 may include furtheropenings adjacent the central piston contact location.

The armature 142 has a tapered surface to define a generallyfrusto-conical shape having a thin cross-section at its outer peripheryor outer pole 147, relative to the cross-section at the inner pole 149.The tapered surface of the armature 142 has a central indentation, inwhich an extended central portion 201 of the cover member 150 extends. Apermanent magnet 202 is disposed within the central portion of the covermember 150 and a magnet cover 204 is attached to the cover member 150,over the magnet 202.

The armature 142 and piston 144 are drawn toward the retracted positionshown in FIG. 3, by the attraction force of the permanent magnet 202. Asa result, a spring (such as spring 46 in the embodiment of FIGS. 3 and4) is not needed. However, further embodiments may employ variouscombinations of one or more permanent magnets and springs for urging thearmature 142 and piston 144 toward the retracted position. In theretracted position, the armature 142 abuts a shoulder 206 on the covermember 150. In further embodiments, instead of abutting shoulders 206,the armature 142 abuts the extended central portion 201 of the covermember 150.

In embodiments employing a magnet 202, the armature 142 may beconfigured with a central section 203 formed of a non-magnetic material,such as stainless steel, biocompatible plastic, ceramic, glass or thelike, to allow the magnetic flux from the magnet 202 to have a greaterattraction action on the piston 144. The portion of the armature 142outward of the central section 203 is preferably made of a magneticallypermeable material, as described above with respect to armature 42. Infurther embodiments, the central section 203 of the armature may beopen. In such embodiments, the central extended portion 201 may includea further extension, shown at 207 in FIG. 13, to provide a stop for thepiston 144 in its retracted or retracted position.

In yet further embodiments, an adjusting plunger, such as plunger 52described above with respect to the embodiment of FIGS. 3 and 4, may bedisposed through the cover member 150 to provide an adjustable stop forthe armature 142 in the retracted position. For example, an adjustmentplunger may extend through an aperture (not shown) formed in the magnet202 or formed elsewhere in the cover member 150, to abut the armature inits retracted position.

In the embodiment of FIGS. 11 and 12, the inlet 127 and inlet port 160extend vertically with respect to the orientation shown in thosefigures. However, other embodiments may employ a horizontal inlet portarrangement with respect to the orientation of the figures, such asshown in FIGS. 3 and 4. Likewise, embodiments as shown in FIGS. 3 and 4may be implemented with a vertical inlet port arrangement as shown inFIGS. 11 and 12. Of course, other suitable inlet port arrangements maybe employed without detracting from further aspects of the drivemechanism described herein.

The outlet chamber 164 in FIGS. 11 and 12 contains a valve assembly 167comprising a valve member 166 and a valve spring 168. The spring 168 isa coil spring, rather than the flat, spiral spring 68 of FIGS. 3 and 4.The coil spring 168 is disposed around a central extended portion 208 ofthe valve cover 172 and, in the retracted position (FIG. 11), extendsbeyond the central extended portion 208 to support the valve member 166in a spaced relation with respect to the central extended portion 208.In the forward position (FIG. 12), the valve member 166 compresses thecoil spring and abuts against the central extended portion 208 of thevalve cover 172. The interior walls of the outlet chamber 164 areprovided with ribs or flutes 209 to help guide the valve member 166between open and closed positions (shown in FIGS. 11 and 12,respectively).

While a coil spring arrangement is shown in FIGS. 11 and 12 and a flatspring arrangement is shown in FIGS. 3 and 4, either a coil or flatspring arrangement may be employed in either of those embodiments. Aflat spring arrangement may provide a thinner form factor and adjustmentcapabilities by selecting or adjusting the thickness of the ring 70, asdescribed above. However, a coil spring arrangement may provide a morestable support for embodiments in which the piston portion of theactuator is separable from the armature portion.

The barrier member 148 in FIGS. 11 and 12 may have folded inner andouter edges 210 and 212, which fold over the inner and outer walls ofthe housing 130. The inner and outer housing walls are formed withannular indentations for receiving the folded edges 210 and 212 of thebarrier member 148. The folded edges of the barrier member enhance thesealing capabilities of the barrier member. In addition, the foldededges allow the barrier member to be welded, or otherwise adhered, tothe housing 130 along a surface 214 on the lateral side of the housing'souter wall. The folded edges allow the barrier to be machined (forexample, lapped) flat, after welding. While a folded edge barrier memberarrangement is shown in FIGS. 11 and 12 and a flat barrier memberarrangement is shown in FIGS. 3 and 4, either a folded edge or flatarrangement may be employed in either of those embodiments.

The drive mechanism 120 operates similar to the drive mechanism 20described above. However, unlike the armature 42 and piston 44 in thedrive mechanism 20, the armature 142 and the piston 144 of the drivemechanism 120 are capable of moving independently and infusion medium isallowed to flow through the passage 145 in the piston when the piston isphysically separated from the armature.

Similar to the embodiment described above, the drive mechanism 120employs electromagnetic and mechanical forces to move between retracted(FIG. 11) and forward (FIG. 12) positions, to cause infusion medium tobe drawn into and driven out of the mechanism in a controlled manner. Inthe retracted position, the magnet 202 urges both the armature 142 andthe piston 144 toward their retracted positions shown in FIG. 11. Inthis position, a central portion 203 of the armature 142 contacts thepiston 144 and blocks one end of the passage 145 in the piston 144. Inthis manner, when the piston 144 and armature 142 are in retractedpositions, the armature 142 blocks the flow of fluid through the passage145 in the piston 144 and, thus, inhibits back flow of fluid from theoutlet chamber side of the piston.

When the coil 138 is energized, the armature 142 is attracted to thecoil cup 138 by electromagnetic flux as described above. The attractionforce is sufficient to overcome the force of magnet 202 and cause thearmature to move and close the gap in the electromagnetic flux pathbetween the armature 142 and the coil cup 132. As the piston 144 is incontact with the armature 142, the piston also moves, reducing thevolume of the piston chamber 165. During movement of the armature andpiston toward their forward positions, the central portion 203 of thearmature 142 remains in contact with the piston 144 and continues toblock the passage 145 and inhibit back flow of fluid from the pistonchamber 165. As the piston 144 moves toward its forward position, thepressure in the piston chamber 165 increases until it is sufficient toovercome the force of the spring 168 and move the valve member 166 tothe open position. When the valve member is opened, infusion mediumwithin the piston chamber 165, passage 145 and within the volume betweenthe piston 144 and the wall of the channel 135 is discharged into theoutlet chamber and through the outlet port 174.

The piston 144 continues to move under the force of the armature 142until the armature 142 contacts the barrier 148 or a mating face (notshown) of the housing 130 or cover 150. When the armature stops, thepiston 144 is in preferably in close proximity or contact with the valvemember 166, to inhibit migration of bubbles into the piston chamber asdescribed above and, thereby, improve self priming capabilities. Alsofor improving self priming capabilities, it is preferred that the totalullage, determined as the sum of the volume of the passage 145 throughthe piston and the volume between the piston and the valve member whenthe piston is in the forward stroke position (FIG. 12), be about 25% ofthe volume of the piston chamber 165 in the retracted or retractedposition (FIG. 11). As described above, a mechanically actuated checkvalve may be provided in the valve member 166 or in the passage 145 ofthe piston, to vent gas from the piston chamber 165 and, thus, furtherimprove the self priming capabilities of the drive mechanism.

When the coil 138 is de-energized, the ferro-magnetic armature 142 andpiston 144 attracted by the magnet 202, to move from the forward strokeposition of FIG. 11, toward the retracted or retracted position of FIG.12. However, due to viscous drag caused by the close proximity of theouter surface of the piston 144 and the surface of the channel 135 wall,the piston returns to the retracted position at a slower rate than thearmature 142. As a result, the armature 142 separates from the piston144 and opens the passage 145 in the piston to the infusion mediumpresent in the interior 151 of the cover member 150. In this manner,during the return stroke, infusion medium from the cover interior 151 isdrawn into the passage 145 through the piston 144 and into the pistonchamber 165.

As the piston 144 moves to the retracted position, the pressure withinthe piston chamber 165 reduces to help draw medium into the pistonchamber and to allow the valve member 166 to close. After the piston 144completes its return stroke, it is again in contact with the armature142 and the passage 145 in the piston is again blocked by the armature142. The piston is then ready for its next forward stroke.

Further Embodiments

While embodiments described above may include valve assemblies 67 and167, as shown in the FIGS. 3, 4, 11 and 12, other embodiments may employother suitable valve assembly structures. For example, in a furtherembodiment, the valve assembly structure may be assembled separatelyfrom the rest of the drive mechanism and, then, connected, as a unitarystructure, to the drive mechanism housing. A representive example of apre-assembled, unitary valve assembly structure 215 is shown in FIG. 14,where the valve assembly 215 includes a valve member 216 having a rigidportion 217 and a resilient portion 218, similar to the valve member 66described above. The valve assembly 215 also includes a valve spring 219similar to the valve spring 68 described above. The valve assembly 215further includes a threaded valve cap 220 in which the spring 219 andthe valve member 216 are disposed. The valve spring 219 supports thevalve member 216 for movement within the valve cap 220. The valveassembly, including the threaded valve cap 220, the spring 219 and thevalve member 216 may be assembled together to form a unitary structure,for example, during or prior to the assembly of the rest of the drivemechanism.

The valve cap 220 may be composed of any suitable biocompatible andinfusion medium compatible material, including, but not limited tostainless steel, titanium, biocompatible plastic, ceramic, glass or thelike, and includes a threaded outer peripheral surface 222, which isconfigured to engage a correspondingly threaded inner peripheral surface224 of an aperture formed in the drive device housing 30 (or 130).Alternatively, the threaded aperture may be formed in a valve cover (72or 172 shown in FIGS. 3 and 11). Thus, once the valve assembly 215 isassembled into a unitary structure, the unitary valve assembly may becoupled to the rest of the rest of the drive mechanism, by threading thevalve assembly into the threaded aperture of the drive mechanism housingor valve cover, as shown in FIG. 15. In alternative embodiments, thevalve assembly may be coupled to the housing or valve cover by othersuitable coupling methods, including, but not limited to, adhesives,welds, brazing or the like. An O-ring seal or other suitable sealingmaterial 226 may be disposed between the valve cap 220 and the housing(or valve cover) to help seal the aperture.

Another embodiment of a valve assembly structure 230 is shown in FIG.16, where the valve assembly 230 includes a valve member 232 having arigid portion 234 and a resilient portion 236. The valve assembly 230also includes a valve spring 238. The valve assembly 230 furtherincludes a valve cap 240 in which the spring 238 and the valve member232 are disposed. The spring 238 supports the valve member 232 formovement within the valve cap 240. The valve assembly, including thevalve cap 240 , the spring 238 and the valve member 236 may be assembledtogether to form a unitary structure, for example, during or prior tothe assembly of the rest of the drive mechanism. Thus, as discussedabove with respect to valve assembly 210, once the valve assembly 230 isassembled into a unitary structure, the unitary valve structure assemblymay be coupled to the rest of the rest of the drive mechanism, bythreading (or otherwise connecting) the valve cap 240 into an aperturein the drive mechanism housing 30 (or 130) or valve cover 72 (or 172).An O-ring seal or other suitable sealing material 236 may be disposedbetween the valve cap 240 and the housing (or valve cover) to help sealthe aperture.

The valve member 232 in the valve assembly 230 includes a stem portion242 which resides within a cylindrical guide 244 in the valve cap 240.The spring 238 abuts the outer peripheral surface of the guide 244. Inthis manner, the guide 244 helps maintain proper alignment of the valveassembly components during manufacture and over the operational life ofthe valve assembly. In addition, the valve assembly 230 includes anannular retainer member 246, which may be composed of any suitablebiocompatible and infusion medium compatible material, including, butnot limited to stainless steel, titanium, biocompatible plastic,ceramic, glass or the like. The annular retainer member 246 provides astop surface for abutting a lip 248 of the valve member 232.

Unitary valve assembly structures, such as valve assemblies 215, 230 orthe like, may be assembled separately from the other components of thedrive mechanism and may be connected, as a pre-assembled structure, tothe housing or valve cover of the drive mechanism during the process ofassembling the drive mechanism. In this manner, unitary valve assemblystructures, such as valve assemblies 215, 230 or the like, may bepre-assembled in bulk to reduce manufacturing costs. Furthermore, suchunitary valve assembly structures may be assembled and tested prior toconnection to other components of the drive mechanism, for example, intesting environments having controlled properties, such as controlledvalve seat dimensions, valve seat pressures, and the like. Moreover,unitary valve assembly structures, such as valve assemblies 215, 230 orthe like, may be coupled to the housing or valve cover of a drivemechanism in an adjustable manner, to adjust the seating force of thevalve member against its valve seat (the valve seat end of the pistonchannel of the drive mechanism). In the above-described embodiments, thevalve seat force may be adjusted by threading the valve cap further intoor further out of the threaded aperture in the housing or valve cover.Other embodiments may employ other suitable adjustment methods,including, but not limited to, a friction fit between the valve cap andthe housing or valve cover.

As described above, valve members 66, 158, 212 and 232 may include anelastomeric, compliant portion for abutting the valve seat and a rigidportion for supporting the compliant portion. Compliant valve materialscan improve sealing capabilities and/or operate with low sealing forces.However, in environments in which it is desirable for each pump stroketo dispense an accurate volume of medium, the compliant portion of thevalve member may introduce errors in the output volume accuracy. Theamount of deflection of the compliant sealing member may significantlyaffect several aspects of the system, including, but not limited to,fluid refill into the piston chamber, amount of ullage or usable volume,interference of the compliant member with the piston, and change theeffective volume of the piston chamber over time.

Therefore, valve members according to further embodiments of theinvention as described with reference to FIGS. 17–22 are configured toprovide the benefits of a compliant valve member, yet reduce oreliminate the above-noted adverse effects on output volume accuracy. Inthe embodiment shown in FIG. 17, a valve member 250 is supported formovement between an open and closed position by a valve spring 251, forexample, in a manner similar to that described above with respect tovalve members 66, 158, 212 and 232 and valve springs 68, 168, 218 and238. The valve member 250 includes a compliant portion 252 supported bya rigid portion or retainer 254. The compliant portion 252 may becomposed of a suitably compliant material such as, but not limited to,an elastomer. The retainer 254 may be composed of a suitably rigid,biocompatible and infusion medium compatible material, such as, but notlimited to, titanium, stainless steel, biocompatible plastic, ceramic,glass, gold, platinum or the like.

The compliant portion 252 in FIG. 17 protrudes a set distance from anextended face of the retainer 254, such that the force of the compliantportion 252 against the valve seat provided by the spring 251 and anyhead pressure (back pressure from the outlet) is sufficient to seal thevalve member 250 against the valve seat. The valve member 250 includesone or more stop surfaces, which may be formed, for example, as one ormore projecting portions of the retainer 254. In the FIG. 17 embodiment,a stop surface 256 comprises the end of an annular wall that extendsaround the circumference of the compliant portion 252. Thus, in the FIG.17 embodiment, the retainer 254, with its annular wall 256, forms a cupfor containing the compliant portion 252. The stop surface on the end ofthe annular wall is located at a position relative to the protrudingposition of the compliant portion such that the force of compliantportion 252 against the valve seat (by spring 251 and any head pressure)is sufficient to compress the protruding compliant portion enough toallow the stop surface 256 to engage the valve seat. The compliantportion 252 may include one or more annular projections 258 surroundingthe end of the piston channel of the drive mechanism, to improve sealingcapabilities of the valve member.

The stop surface 256, thus, provides a hard stop at a pre-definedposition, defined by the position of the stop surfaces. By extending orconfiguring the protruding end of the compliant portion 254, thecompliant portion 254 may form a seal against the valve seat or asurface adjacent the valve seat, at least by the time the stop surface256 makes hard contact with the valve seat or a surface adjacent thevalve seat. Once a seal is formed (between the compliant portion 254 andthe valve seat) and the stop surface 256 of the retainer 254 contactsthe valve seat, further compression of the compliant portion and furthervariances in the piston chamber volume are arrested. As a result, thevalve configuration may provide a pre-determined, accurate andrepeatable piston chamber volume with each valve closure.

In preferred embodiments, the compliant portion 252 forms a seal againstthe valve seat upon the retainer 254 making contact with the valve seator a surface adjacent the valve seat, as shown in FIG. 18.Alternatively, a seal may be formed prior to the retainer 254 makingcontact with the valve seat or a surface adjacent the valve seat, as theprotruding end of the compliant portion 252 compresses against the valveseat, as shown in FIG. 19. For example, design optimization, includingbut not limited to, minimizing load associated with the valve or energyused by the system, may utilize a valve return spring with less force.For that operating condition, the spring may be designed or selected inconjunction with the compliant portion such that the load supplied bythe spring does not fully compress the compliant material. Under certainconditions, a head pressure may be generated on the outlet side of thevalve, forcing the valve retainer 254 to move axially an appropriatedistance to achieve a hard stop of the stop surface 256 against thevalve seat or a surface adjacent the valve seat.

In further valve configuration embodiments as shown in FIG. 20, thevalve seat includes a projecting surface 260 and a recessed surface 262.The recessed surface 262 is positioned to contact the compliant portion252 of the valve member 250 either at the same time as or prior to theprojecting surface 260 making contact with the stop surface 256 of theretainer 254. In yet further valve configuration embodiments as shown inFIG. 21, the valve seat includes one or more annular projections 264(one shown in FIG. 21), for engaging, and preferably compressing, thecompliant portion 252 around the piston channel of the drive mechanism.The retainer 254 may include a stop surface 256 extended beyond thecompliant portion 252, preferably a distance that is not so great as toinhibit the projection 264 from contacting or contacting and compressingthe compliant portion 252 (for example, a distance less than thedistance that the projection 264 projects beyond the valve seat surfacethat makes contact with the stop surface 256).

In yet a further valve configuration embodiment as shown in FIG. 22, atleast one annular compliant member 266 is disposed in the valve seat,surrounding the valve end of the piston channel of the drive mechanism.The compliant member 266 may be molded, press fit or otherwise fixed inplace, for example, in an annular groove in the valve seat, surroundingthe valve end of the piston channel. In the FIG. 22 embodiment, thevalve member 250 need not include a compliant portion. Instead, inpreferred embodiments, the valve member 250 includes at least oneannular projection 268 arranged to engage the complient member(s) 266.The valve member 250 may also include at least one stop surface 256 forcontacting the valve seat and inhibiting further movement of the valvemember in the direction toward the valve seat or a surface adjacent thevalve seat. The stop surface 256 may make contact with the valve seat ora surface adjacent the valve seat upon the projection(s) 268 makingcontact with the compliant member(s) 266 and, more preferably, after theprojection(s) at least partially compresses the compliant member(s) 266.

While drive mechanism embodiments described above employ a coaxialarrangement of the coil, piston channel and piston, other embodimentsmay employ a piston and piston channel located between, but not coaxialwith, a plurality of spaced coils. For example three coils may belocated in a spaced relation at three respective corners of a triangle,with the piston channel and piston located in the center of the triangle(surrounded by the three locations of the coils), and with the pistonaxis parallel to the axes of the coils. In further embodiments more thanthree coils may be located at discrete positions spaced around thepiston (at locations surrounding the piston), preferably, equally spacedfrom the piston or otherwise arranged to provide approximately equalforces on the piston.

While various features are described herein in connection with theembodiment of FIGS. 11 and 12 and further features are described hereinin connection with FIGS. 3 and 4, it is contemplated that, wherepossible, features described in connection with one embodiment may beemployed in the other embodiment. For example, the outlet configurationwith one or more accumulator chambers described above with respect toFIGS. 3 and 4 may be employed in the embodiment of FIGS. 11 and 12.

Alternative Actuator Embodiments

Another example of an actuator member is shown in FIG. 23A, wherein a sbefore, the armature portion 42 of the actuator member has a round, discshape. However, in this embodiment of the actuator member there are novent holes or other openings extending through the actuator member, norare there radial struts coupling the annular outer section 47 to theinner section 49 of the armature. Rather, a solid annular midsection 53couples the annular outer section 47 to the inner section 49. Inaddition, as shown in FIG. 23B, the surface of the actuator member inthis embodiment that comes into contact with medication or other fluidsis covered by a covering material 55. The covering material 55 mayinclude, without limitation, materials exhibiting high corrosionresistance such as titanium, which has a history of use in the art withrespect to medication or other fluid contact and which should, whenwelded to the actuator member, face little regulatory resistance. Thecovering material 55 need not comprise a ferrous material, as long as itcovers a ferrous material. In addition to being welded to the actuatormember, the covering material 55 may be plated or coated onto theactuator member.

Although the midsection 53 shown in FIG. 23A is solid, in otherembodiments it need not be. For example, an embodiment of the midsection53 may be made with openings extending through it. However, in such anembodiment, the covering material 55, would also be made withcorresponding openings, thereby providing a path through which themedication or other fluid may travel.

Yet another example of an actuator member is shwon in FIG. 24, wherein,again, the armature portion 42 of the actuator member has a round, discshape. As can be seen, in this embodiment the midsection 53 is formedwith a plurality of through-holes 57. The through-holes 57 may besubstantially round and evenly spaced around the midsection 53. Thistype of through-hole 57 provides less area through which medication orother fluid may pass than the type of openings shown in FIG. 9. In otherwords, the amount of venting is decreased, which generally results ingreater power consumption by the device. However, the embodiment of FIG.24 is generally less expensive to manufacture than the embodiment shownin FIG. 9. In addition, the embodiment of the actuator member shown inFIG. 25 typically makes less noise than the embodiment shown in FIG. 9,The through-holes 57 need not be round, however; they may be elongatedor some other geometry. The through-holes 57 may be laser cut into themidsection 53.

In the embodiment of the actuator member shown in FIG. 24, the diameterand, consequently, the area of the inner section 49 has been increasesuch that greater damping is achieve while consuming less power. Thus,in FIG. 25, during the first part of the stroke in a pumping operation,medication or other fluid flows radially outward relatively easily.Toward the end of the stroke, the operation of the actuator member issimilar to that of a valve closing. Fluid begins to flow through thethrough-holes 57 and the CV becomes a function of the stroke. Dampingoccurs right at the end of the stroke, slowing the actuator down,reducing mechanical impact and decreasing power consumption.

The foregoing description of the preferred embodiment of the inventionhas been presented for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed. Many modifications and variations are possiblein light of the above teaching.

1. A drive mechanism for delivery of infusion medium comprising: aninlet for receiving infusion medium; a piston channel for communicationof infusion medium received by the inlet; a coil surrounding the pistonchannel; a piston located within the piston channel and moveable axiallywithin the piston channel to drive infusion medium into the pistonchannel; and an armature disposed adjacent the coil, on one side of thepiston channel, the armature having a pair of pole surfaces and alsohaving radial struts for conducting electromagnetic flux between thepole surfaces in a radial direction; wherein a clearance between thepiston and the piston channel causes a volume of the infusion medium forrefilling the piston channel to be greater than a volume of the infusionmedium backflowing through the piston channel.
 2. A drive mechanism asrecited in claim 1, further comprising a coil cup composed of amagnetizable material, the coil cup having: a generally annular innerwall; a generally annular outer wall; a generally annular interiorbetween the inner and outer walls, the annular interior containing thecoil; and a piston channel surrounded by the inner wall, the pistonchannel of the coil cup being substantially coaxial with the coil;wherein the inner wall has one end defining an inner pole surface andthe outer wall has a second end defining an outer pole surface, theinner and outer pole surfaces acting with the armature to provide anelectromagnetic flux path upon electrical activation of the coil.
 3. Adrive mechanism as recited in claim 2, further comprising a housinghaving a generally annular cavity containing the coil cup, the housingfurther having a central channel defining the piston channel.
 4. A drivemechanism as recited in claim 3, wherein the housing is open on one sideto the generally annular cavity and has a further cavity disposed on theopposite side, the further cavity defining an outlet chamber.
 5. A drivemechanism as recited in claim 3, wherein the coil cup is secured to thehousing by a friction fit of the coil cup within the generally annularcavity of the housing.
 6. A drive mechanism as recited in claim 2,further comprising: a housing having an interior cavity containing thecoil cup, the housing further having a central channel defining thepiston channel, the housing being open on one side to the interiorcavity; and a cover member disposed over the open side of the housing,the cover member defining an interior volume in which the armature ismoveably disposed; wherein said inlet is in flow communication with theinterior volume of the cover member.
 7. A drive mechanism as recited inclaim 6, further comprising means for urging the armature in an axialdirection toward the cover member toward a retracted position, whereinthe cover member includes at least one stop surface for contacting thearmature in the retracted position.
 8. A drive mechanism as recited inclaim 7, wherein the means for urging comprises a spring.
 9. A drivemechanism as recited in claim 7, wherein the means for urging comprisesa magnet disposed within the cover member.
 10. A drive mechanism asrecited in claim 2, further comprising: a housing having a cavitycontaining the coil cup, the housing having a central channel thatdefines the piston channel, the housing having a further cavity disposedon one end of the piston channel, wherein the further cavity defines anoutlet chamber; a valve member moveable between open and closedpositions to selectively open and close one end of the piston channel tothe outlet chamber; and a valve spring for urging the valve member inthe closed position; wherein the valve member and valve spring arelocated within the further cavity defining the outlet chamber.
 11. Adrive mechanism as recited in claim 1, further comprising means forurging the armature and piston to move in an axial direction away fromthe outlet chamber.
 12. A drive mechanism as recited in claim 11,wherein the means for urging comprises a spring.
 13. A drive mechanismas recited in claim 11, wherein the means for urging comprises a magnet.14. A drive mechanism as recited in claim 1, further comprising a valvemember moveable between open and closed positions to selectively allowand inhibit fluid flow between the inlet and the outlet, the valvemember being moveable in response to axial movement of the piston withinthe piston channel.
 15. A drive mechanism as recited in claim 1, furthercomprising a valve member moveable between open and closed positions toselectively open and close one end of the piston channel to an outletchamber, the valve member being moveable in response to axial movementof the piston within the piston channel.
 16. A drive mechanism asrecited in claim 15, wherein the piston is moveable in the axialdirection of the channel between a retracted position and a forwardposition, wherein the valve member is located in the closed positionwhen the piston is in the retracted position and wherein the valvemember is moved to the open position when the piston is moved to theforward position.
 17. A drive mechanism as recited in claim 15, whereinthe piston is moveable in the axial direction of the piston channelbetween a retracted position and a forward position such that, upon thepiston being in the retracted position, a volume is defined between thepiston and the valve member for receiving infusion medium through thepiston channel and, upon the piston thereafter being moved toward theforward position, the volume between the piston and the valve memberdecreases to increase infusion medium pressure within the volume, forcethe valve member to the open position and discharge infusion medium intoan outlet chamber.
 18. A drive mechanism as recited in claim 1, furthercomprising a housing containing the coil and an outlet chamber, thehousing having at least one fluid flow damping means or accumulatordisposed in a flow path between the outlet chamber and the outlet, forreducing flow pressure variations.
 19. A drive mechanism as recited inclaim 18, wherein said at least one damping means comprises at least onecompressible member disposed within the flow path.
 20. A drive mechanismas recited in claim 18, wherein said at least one damping meanscomprises at least one chamber containing at least one compressiblepillow.
 21. A drive mechanism as recited in claim 18, wherein said atleast one damping means comprises a plurality of chambers, eachcontaining at least one compressible pillow.
 22. A drive mechanism asrecited in claim 1, further comprising: a valve member moveable betweenopen and closed positions to selectively open and close one end of thepiston channel to an outlet chamber; and a valve spring for urging thevalve member in the closed position; wherein the valve member and valvespring are located within the outlet chamber.
 23. A drive mechanism asrecited in claim 1, wherein the piston and armature are composed of asingle, unitary structure.
 24. A drive mechanism as recited in claim 23,wherein the piston has two ends spaced apart in the axial direction anda flow passage extending in the axial direction from one end of thepiston to the other end of the piston.
 25. A drive mechanism as recitedin claim 1, wherein the piston and armature are composed of separablestructures and are moveable independent of each other.
 26. A drivemechanism as recited in claim 1, further comprising: a valve membermoveable between open and closed positions to selectively open and closeone end of the piston channel to an outlet chamber, the valve memberbeing moveable in response to axial movement of the piston within thepiston channel; wherein the piston has two ends spaced apart in theaxial direction and a flow passage extending in the axial direction fromone end of the piston to the other end of the piston; and wherein thepiston is moveable in the axial direction of the channel between aretracted position and a forward position such that, upon the pistonbeing in the retracted position, a volume is defined between the pistonand the valve member for receiving infusion medium through the passagein the piston and, upon the piston thereafter being moved toward theforward position, the volume between the piston and the valve memberdecreases to increase infusion medium pressure within the volume, forcethe valve member to the open position and discharge infusion medium intothe outlet chamber.
 27. The drive mechanism of claim 1, wherein thevolume of the infusion medium for refilling the piston channel is about1 to 4 times greater than the volume of the infusion medium backflowingthrough the piston channel.
 28. The drive mechanism of claim 1, whereina ratio of a diameter of the piston to a diameter of the piston channelis within a range of about 0.990 to about 0.995.
 29. The drive mechanismof claim 1, wherein the clearance between the piston and the pistonchannel averages about 250 microinches.
 30. The drive mechanism of claim1, further comprising: a valve member being moveable in response toaxial movement of the piston within the piston channel, wherein aclearance between the piston and the piston channel is sufficient torestrict the infusion medium within the piston channel such thatpressure on the infusion medium caused by movement of the piston opensthe valve member.
 31. The drive mechanism of claim 1, furthercomprising: an outlet chamber disposed adjacent the coil, on theopposite side of the piston channel relative to the armature forreceiving infusion medium from the channel; and an outlet in flowcommunication with the outlet chamber, for discharging infusion mediumfrom the outlet chamber.
 32. A drive mechanism for delivery of infusionmedium comprising: an inlet for receiving infusion medium; a pistonchannel for communication of infusion medium received by the inlet; acoil surrounding the piston channel; a piston located within the pistonchannel and moveable axially within the piston channel to drive infusionmedium into the piston channel; and an armature disposed adjacent thecoil, on one side of the piston channel, wherein a clearance between thepiston and the piston channel causes a volume of the infusion medium forrefilling the piston channel to be greater than a volume of the infusionmedium backflowing through the piston channel; wherein the coil iscapable of being electrically activated to provide an electromagneticfield; wherein the armature is moveable toward the coil, in response tothe electromagnetic field produced by an activation of the coil; andwherein the armature comprises radial struts for conductingelectromagnetic flux in a radial direction.
 33. A drive mechanism fordelivery of infusion medium comprising: an inlet for receiving infusionmedium; a piston channel for communication of infusion medium receivedby the inlet; a coil surrounding the piston channel; a piston locatedwithin the piston channel and moveable axially within the piston channelto drive infusion medium into the piston channel; and an armaturedisposed adjacent the coil, on one side of the piston channel, wherein aclearance between the piston and the piston channel causes a volume ofthe infusion medium for refilling the piston channel to be greater thana volume of the infusion medium backflowing through the piston channel;wherein the armature has an annular inner pole surface and an annularouter pole surface, each made of a magnetizable material, wherein theinner pole surface of the armature faces the inner pole surface of theinner coil cup wall, and outer pole surface of the armature faces theouter pole surface of the outer coil cup wall.
 34. A drive mechanism asrecited in claim 33, wherein the armature further has a plurality ofradial struts made of magnetizable material coupling the inner and outerpole surfaces of the armature.
 35. A drive mechanism as recited in claim34, wherein the armature further has apertures between the radialstruts.
 36. A drive mechanism as recited in claim 33, wherein at leastone of the inner and outer pole surfaces of the armature are textured.37. A drive mechanism as recited in claim 33, wherein the inner polesurface of the armature is spaced from the inner cup wall by a first gapand the outer pole surface is spaced from the outer cup wall by a secondgap when the coil is not electrically activated, and wherein the secondgap is larger than the first gap.
 38. A drive mechanism for delivery ofinfusion medium comprising: an inlet for receiving infusion medium; atleast one coil capable of being electrically activated to provide anelectromagnetic field, the at least one coil surrounding an axial pistonchannel that provides a passage for communication of infusion mediumreceived by the inlet; an armature disposed adjacent the coil, on oneside of the axial piston channel and moveable in a first directionrelative to the coil, in response to the electromagnetic field producedby an activation of the coil, the armature having a pair of polesurfaces and also having radial struts for conducting electromagneticflux between the pole surfaces in a radial direction; and a pistonlocated within the piston channel and moveable axially within thechannel in the first direction, in response to movement of the armature,wherein a clearance between the piston and the piston channel causes avolume of infusion medium for refilling the piston channel to be greaterthan a volume of infusion medium backflowing through the piston channel.39. The drive mechanism of claim 38, further comprising: an outletchamber disposed adjacent the coil, on the opposite side of the pistonchannel relative to the armature for receiving infusion medium from thepiston channel, upon movement of the piston in the first direction; andan outlet in flow communication with the outlet chamber, for discharginginfusion medium from the outlet chamber.
 40. An infusion device fordelivering infusion medium, the device comprising: a housing having anoutlet through which infusion medium may be discharged; a reservoirdisposed within the housing, for containing a volume of infusion medium;a control circuit for providing drive control signals; a drive mechanismdisposed within the housing, for driving infusion medium from thereservoir and out the outlet, in response to drive control signals fromthe control circuit; and a power source disposed within the housing, forproviding power to the control circuit and drive mechanism; wherein thedrive mechanism comprises: an inlet for receiving infusion medium fromthe reservoir; at least one coil capable of being electrically activatedto provide an electromagnetic field in response to a signal from thecontrol circuit, the at least one coil surrounding an axial pistonchannel that provides a passage for communication of infusion mediumreceived by the inlet; an armature disposed adjacent the coil, on oneside of the axial channel and moveable in a first direction relative tothe coil, in response to the electromagnetic field produced by anactivation of the coil, the armature having a pair of pole surfaces andalso having radial struts for conducting electromagnetic flux betweenthe pole surfaces in a radial direction; and a piston located within thepiston channel of the coil and moveable axially within the channel inthe first direction, in response to movement of the armature, wherein aclearance between the piston and the piston channel causes a volume ofinfusion medium for refilling the piston channel to be greater than avolume of infusion medium backflowing through the piston channel. 41.The infusion device of claim 40, wherein the drive mechanism furthercomprises: an outlet chamber disposed adjacent the coil, on the oppositeside of the piston channel relative to the armature for receivinginfusion medium from the piston channel, upon movement of the piston inthe first direction; and an outlet port in flow communication with theoutlet chamber and the housing outlet, for discharging medium from theoutlet chamber, through the housing outlet.
 42. A drive mechanism fordelivery of infusion medium comprising: an inlet for receiving infusionmedium; a piston channel for communication of infusion medium receivedby the inlet; a coil surrounding the piston channel; a piston locatedwithin the piston channel and moveable axially within the piston channelto drive infusion medium into the piston channel; an armature disposedadjacent the coil, on one side of the piston channel; an outlet chamberdisposed adjacent the coil, on the opposite side of the piston channelrelative to the armature for receiving infusion medium from the channel;and an outlet in flow communication with the outlet chamber, fordischarging infusion medium from the outlet chamber, wherein the coil iscapable of being electrically activated to provide an electromagneticfield; wherein the armature is moveable toward the coil, in response tothe electromagnetic field produced by an activation of the coil; andwherein the armature comprises radial struts for conductingelectromagnetic flux in a radial direction.
 43. A drive mechanism fordelivery of infusion medium comprising: an inlet for receiving infusionmedium; a piston channel for communication of infusion medium receivedby the inlet; a coil surrounding the piston channel; a piston locatedwithin the piston channel and moveable axially within the piston channelto drive infusion medium into the piston channel; a coil cup containingthe coil, the coil cup having an inner pole surface and an outer polesurface; an armature disposed adjacent the coil, on one side of thepiston channel; an outlet chamber disposed adjacent the coil, on theopposite side of the piston channel relative to the armature forreceiving infusion medium from the channel; and an outlet in flowcommunication with the outlet chamber, for discharging infusion mediumfrom the outlet chamber, wherein the armature has an annular inner polesurface and an annular outer pole surface, each made of a magnetizablematerial, and wherein the inner pole surface of the armature faces theinner pole surface of the coil cup, and the outer pole surface of thearmature faces the outer pole surface of the coil cup.